The BNC (Bayonet Neill–Concelman) connector is a miniature quick connect/disconnect radio frequency connector used for coaxial cable. It features two bayonet lugs on the female connector; mating is fully achieved with a quarter turn of the coupling nut. BNC connectors are used with miniature-to-subminiature coaxial cable in radio, television, and other radio-frequencyelectronic equipment, test instruments, and video signals. The BNC was commonly used with 10BASE2 computer networks. BNC connectors are made to match the characteristic impedance of cable at either 50 ohms or 75 ohms. They are usually applied for frequencies below 4 GHz[1] and voltages below 500 volts.[2]

Similar connectors using the bayonet connection principle exist, and a threaded connector is also available. United States military standard MIL-PRF-39012 entitled Connectors, Coaxial, Radio Frequency, General Specification for (formerly MIL-C-39012) covers the general requirements and tests for radio frequency connectors used with flexible cables and certain other types of coaxial transmission lines in military, aerospace, and spaceflight applications.[3]

The BNC was originally designed for military use and has gained wide acceptance in video and RF applications to 2 GHz. The BNC uses a slotted outer conductor and some plastic dielectric on each gender connector. This dielectric causes increasing losses at higher frequencies. Above 4 GHz, the slots may radiate signals, so the connector is usable, but not necessarily stable up to about 11 GHz. Both 50 ohm and 75 ohm versions are available. The BNC connector is used for signal connections such as:

The BNC connector is used for composite video on commercial video devices. Consumer electronics devices with RCA connector jacks can be used with BNC-only commercial video equipment by inserting an adapter. BNC connectors were commonly used on 10base2 thin Ethernet network cables and network cards. BNC connections can also be found in recording studios. Digital recording equipment uses the connection for synchronization of various components via the transmission of word clock timing signals.

Typically the male connector is fitted to a cable, and the female to a panel on equipment. Cable connectors are often designed to be fitted by crimping[4] using a special power or manual tool.[5]Wire strippers which strip outer jacket, shield braid, and inner dielectric to the correct lengths in one operation are used.[6]

The basis for the development of the BNC connector was largely the work of Octavio M. Salati, a graduate of the Moore School of Electrical Engineering of the University of Pennsylvania. In 1945, while working at Hazeltine Electronics Corporation, he filed a patent for a connector for coaxial cables that would minimize wave reflection/loss. The patent was granted in 1951.[8]

BNC connectors are most commonly made in 50 and 75 ohm versions, matched for use with cables of the same characteristic impedance. The 75 ohm types can sometimes be recognized by the reduced or absent dielectric in the mating ends but this is by no means reliable. There was a proposal in the early 1970s for the dielectric material to be coloured red in 75 ohm connectors, and while this is occasionally implemented, it did not become standard. The 75 ohm connector is dimensionally slightly different from the 50 ohm variant, but the two nevertheless can be made to mate. The 50 ohm connectors are typically specified for use at frequencies up to 4 GHz and the 75 ohm version up to 2 GHz. A 95 ohm variant is used within the aerospace sector, but rarely elsewhere. It is used with the 95 ohm video connections for glass cockpit displays on some aircraft.[citation needed]

Reverse-polarity BNC (RP-BNC) is a variation of the BNC specification which reverses the polarity of the interface. In a connector of this type, the female contact normally found in a jack is usually in the plug, while the male contact normally found in a plug is in the jack. This ensures that reverse polarity interface connectors do not mate with standard interface connectors.[2] The SHV connector is a high-voltage BNC variant that uses this reverse polarity configuration.

Smaller versions of the BNC connector, called Mini BNC and High Density BNC (HD BNC), are manufactured by Amphenol. While retaining the electrical characteristics of the original specification, they have smaller footprints giving a higher packing density on circuit boards and equipment backplanes. These connectors have true 75 ohm impedance making them suitable for HD video applications.

The different versions are designed to mate with each other,[2] and a 75 ohm and a 50 ohm BNC connector which both comply with the 2007 IEC standard, IEC 60169-8,[9] will mate non-destructively. At least one manufacturer[10] claims very high reliability for the connectors' compatibility.

At frequencies below 10 MHz the impedance mismatch between a 50 ohm connector or cable and a 75 ohm one has negligible effects.[11] BNC connectors were thus originally made only in 50 ohm versions, for use with any impedance of cable. Above this frequency, however, the mismatch becomes progressively more significant and can lead to signal reflections.

A BNC inserter/remover tool also called a BNC tool, BNC extraction tool, BNC wrench, or BNC apple corer, is used to insert or remove BNC connectors in high density or hard-to-reach locations, such as densely wired patch panels in broadcast facilities like central apparatus rooms.

In the USSR, BNC connectors were copied as SR connectors. As a result of recalculating from imperial to metric measurements their dimensions differ slightly from those of BNC. They are however generally interchangeable with them, sometimes with force applied.

Twin BNC (also known as twinax) connectors use the same bayonet latching shell as an ordinary BNC connector but contain two independent contact points (one male and one female), allowing the connection of a 78 ohm or 95 ohm shielded differential pair such as RG-108A.[13] They can operate up to 100 MHz and 100 volts. They cannot mate with ordinary BNC connectors. An abbreviation for twinax connectors has been BNO (Sühner).

Triaxial (also known as triax) connectors are a variant on BNC that carry a signal and guard as well as ground conductor. These are used in sensitive electronic measurement systems. Early triaxial connectors were designed with just an extra inner conductor, but later triaxial connectors also include a three-lug arrangement to rule out an accidental forced mating with a BNC connector. Adaptors exist to allow some interconnection possibilities between triaxial and BNC connectors. The triaxial may also be known as a Trompeter connection.

For higher voltages (above 500 V), MHV and SHV connectors are typically used. MHV connectors are easily mistaken for BNC type, and can be made to mate with them by brute force. The SHV connector was developed as a safer alternative, it will not mate with ordinary BNC connectors and the inner conductor is much harder to accidentally contact.

BNC connectors are commonly used in electronics, but in some applications they are being replaced by LEMO 00 miniature connectors which allow for significantly higher densities. In video broadcast industry, the DIN 1.0/2.3 and the HD-BNC connector are used for higher density products

^Canford. "In over 15 years and many million BNC connectors we have no first hand experience of incompatibility between 50 ohm and 75 ohm types, other than extremely rare (and very obvious) manufacturing faults."